It is known that electrical power can be harvested from wind energy using wind turbines. Control of the turbine blade pitch is often utilized for creating optimum turbine loading conditions in order to harvest the wind energy with the highest possible efficiency. One concern that the operators of the turbines face is that fluctuating and non-uniform wind conditions can fatigue and damage components associated with the turbine, including the main shaft, the tower, and the rotor blades. Asymmetrical loading across the rotors (for example, due to wind shear, turbulence, and yaw misalignment) can create non-uniform load distributions on the blades of the rotor which may in turn reduce the power conversion efficiency or even lead to costly damages of the turbine components. It is therefore necessary to control the pitch of the turbine blades to keep the wind load on each blade within safe operational limits while maximizing the wind power conversion. To address these issues, systems and methods are needed for controlling the turbine blade pitch based on the angular position of the turbine rotor.
Previous systems have been proposed for determining the phase angle of the rotor by the use of an absolute encoder placed at the end of the rotor slip ring. However, if the rotor tower top is bending and moving, measurement errors may be introduced due to differences in the frame of reference between the encoder and the turbine rotor. Other systems have been proposed where three one-dimensional accelerometers are fixed to the rotor and placed at equidistant angles around the rotation axis of the rotor for removal of the tangential acceleration components. However, such systems require additional mounting, precise positioning, and additional wiring for the three accelerometers.
A need remains for improved systems and methods for determining the angular position of a wind turbine rotor.